A. Field of the Invention
The present invention relates to wide area lighting systems which utilize a plurality of light fixtures elevated at substantial heights relative to an area or volume of space to be lighted. Examples are disclosed at U.S. Pat. No. 4,816,974; U.S. Pat. No. 5,211,473; U.S. Pat. No. 5,161,883; U.S. Pat. No. 5,707,142; US publication No. 2006/0198145, now U.S. Pat. No. 7,458,700; US publication No. 2006/0176695; US publication No. 2006/0181882; and US publication No. 2006/0181875, now U.S. Pat. No. 7,789,540. In particular, the invention relates to methods and apparatus to provide direct illumination on aerial objects or to a volume of aerial space, control the direction and intensity of light to reduce glare for viewers within the target area, and reduce glare and spill light outside the target area.
B. Issues in the Present State of the Art
In relatively recent times, substantial effort has gone into the development of methods to counter-act spill and glare light concerns in wide area lighting installations. Glare and spill light, and halo effect light, are referred to by some as light pollution. Sometimes lighting systems are not allowed to be installed and operated unless they meet glare and spill light restrictions or regulations. These restrictions and regulations can be quite stringent.
Light pollution remediation methods also, therefore, have to be quite stringent. State of the art glare and spill light control methods may meet glare and spill restrictions or regulations, but do not always adequately address aerial illumination needs. Or they do not always do so efficiently or economically. A good example is sports lighting. To meet glare and spill requirements, illumination levels above the playing field might be attenuated to the extent it affects playability. By playability, it is meant that there may be insufficient illumination of the volume of space, or parts of it, above a playing field for the players to follow, for example, the flight of a ball. Glare and spill light control usually involves attenuation or redirection of light, which can remove or prevent light from adequate illumination of relevant aerial space.
Similar issues of inadequate aerial illumination can exist for other type of wide-area or flood lighting. There may be situations where general wide area lighting requires aerial viewing of fixed or moving objects. An example might be illumination of tall monuments, or other elevated or vertically tall objects. Another example might be security lighting. As can be appreciated, glare and spill light control may affect either the amount or consistency of aerial illumination for similar reasons as discussed above regarding sports lighting.
On the other hand, some state of the art lighting products provide adequate aerial illumination but do not adequately address glare and spill light. With respect to sports lighting as an example, some conventional sports lighting fixtures utilize symmetrical bowl-shaped reflectors and high intensity discharge (HID) lamps centered along the axis of revolution of the reflector. While this long-used, conventional-type fixture provides a relatively controlled and concentrated beam for use with other such fixtures in providing illumination of an entire playing field, the symmetry of the reflector results in light reflecting upwardly and outwardly from the lower hemisphere. As a result, this can produce an adequate level of direct aerial lighting over the playing field. However, it can also produce glare and spill light. Some of the light can project to sites off the playing field. Glare can exist for on-site spectators or off-site viewers of the lights.
Therefore, providing both adequate lighting, including effective aerial lighting from multiple fixtures, as well as controlling lighting issues such as glare, spill light, and up-light from high intensity wide area lighting, is difficult to achieve. Designs and methods for addressing one of these aspects are often in direct conflict with another of these aspects.
More specifically, glare and spill light are well-known and significant issues for high intensity wide area lighting. In the wide-area lighting example of sports lighting, such lights are typically elevated high into the air (usually at least 35 feet, and more likely 70 to 120 feet or more) and they can also be relatively distant from their target (hundreds of feet). Light, by basic laws of physics, tends to disperse with distance. While state of the art high intensity sports lighting is designed to try to capture and control as much light as possible to the target, and uses relatively narrow, concentrated beams for those purposes, some light tends to spill off the target (e.g. the playing field). Also, many times observers located quite a distance away from the lights and the target, as well as observers near the target, have a direct view of either the light source or the reflective surface of at least one fixture, and sometimes more than one. The high power and nature of these lamps and fixtures can produce a significant glare effect to such observers, especially since glare intensity (candlepower) does not diminish with distance; unlike illumination which diminishes in proportion to the square of the distance (i.e. foot-candles at a given point is calculated by dividing candlepower by the distance squared). These issues are well-known in the art.
To counter-act problems with spill and glare from high intensity wide area lighting fixtures, a variety of products have been attempted or developed by a variety of companies. Some specific glare and spill light control products and methods have been developed by MUSCO® Corporation of Oskaloosa, Iowa USA. Examples can be found with commercially available products such as SPORTCLUSTER-2®™, TOTAL LIGHT CONTROL™ (or TLC™), LEVEL-8™, and LIGHT-STRUCTURE GREEN™ systems from MUSCO® Corporation and/or U.S. patents such as U.S. Pat. No. 4,816,974; U.S. Pat. No. 5,211,473; U.S. Pat. No. 5,161,883; U.S. Pat. No. 5,707,142.
Many of these methods use the conventional bowl-shaped reflector. Some add a visor for glare and spill control. But, as discussed in more detail later, to achieve glare and spill control, such visors tend to block, attenuate, or render unusable a substantial amount of light.
Some glare and spill control methods alter or configure the bottom hemisphere of a symmetrical, bowl-shaped lighting fixture to reflect more light downward to the target which might otherwise go outside the target. An example is the SPORTSCLUSER-2®™ fixture commercially available from MUSCO® Corporation. It tends to reduce glare and spill with this modification. However, without a visor, it does tend to also allow an amount of direct aerial light that is generally sufficient for playability. However, it may not have sufficient glare and spill control for at least certain applications. Therefore, some methods have been developed to provide a greater degree of glare and spill light control than fixtures without visors.
Some attempts, like louvers across the front opening or lens of the fixture, may work towards control of spill or glare, but essentially block light from exiting the fixture, which decreases their efficiency. In some cases it makes them literally impractical for use due to decreased efficiency. A reduction in light of significant amount from plural fixtures can require more light fixtures to meet light intensity and uniformity requirements of many applications, including for example sports lighting. Increasing the number of fixtures can greatly increase capital as well as operating costs for the lighting system. An example of louvers across the front of a fixture is shown and described at U.S. Pat. No. 5,707,142. Louvers 32 and 34 would block direct view of HID lamp 20 from many viewing angles, but would also block or make essentially unusable a portion of light that might otherwise project outside the playing field. U.S. Pat. No. 5,707,142 also discloses a visor 76 with an extension or outer louver 78. They would also tend to block or absorb light and decrease the efficiency of the fixture.
Some attempts use different types of visors, which also tend to block or absorb or do not effectively or efficiently redirect light from the fixture to increase glare or spill light control, as well as halo light (another form of light pollution well known in the art). However, this can likewise decrease efficiency of the fixtures and can make them less practical. The blocked or absorbed, or inefficiently directed light would not be available to illuminate the target. Examples include U.S. Pat. No. 4,816,974; U.S. Pat. No. 5,211,473; U.S. Pat. No. 5,161,883; U.S. Pat. No. 5,707,142, and/or commercially available TLC™ and LEVEL-8™ brands from MUSCO® Corporation. Many of these systems, e.g. TLC™ brand, can control glare and spill very well, but mid-field playability may sometimes be insufficient. TLC™ utilizes a blackened visor that has a distal portion that extends downward and then outward (like shown in FIGS. 1 and 3 of U.S. Pat. No. 5,707,142). This can block or absorb significant light which is usually beneficial for glare and spill control, but not for efficiency or aerial lighting. The visor extension also does not efficiently redirect light that otherwise might otherwise project up and out and be spill or aerial lighting. The visor and extension also address glare by some blocking direct view of the light source in the fixture from many on-site or off-site viewing directions. But all this can be at the expense of loss of direct aerial lighting. It can also be at the expense of loss of efficiency for the fixture or lighting system. MUSCO® Corporation Level-8™ brand fixtures, for example, can provide a good combination of glare and spill control with generally adequate mid-field playability. As can be seen at U.S. Pat. No. 5,211,473 and U.S. Pat. No. 5,161,883, for example, Level-8™ can include louvers or other members inside the visor, but the efficiency of such a fixture may be less than desirable for certain applications. By reference to U.S. Pat. No. 5,211,473 and U.S. Pat. No. 5,161,883, a variety of visors, in combination with a reformed lower hemisphere, are shown. For even more glare and spill control, visors (e.g. FIG. 27, ref. nos. 234 and 238 of U.S. Pat. No. 5,211,473), and louvers (e.g. FIG. 30, ref. nos. 246 and 256 of U.S. Pat. No. 5,211,473) are utilized. As can be seen, these internal louvers can serve to block light, other disperse light, that otherwise might project outward and upward, and block direct view of the light source for some viewers. Because, unlike TLC™, it is not almost a complete block, more direct aerial lighting can be produced. However, the louvers are angled relative to the direction of light from the fixture to block some direct view of the HID lamp, but also block or absorb some light or render it effectively not useable for the target or for aerial lighting. This can raise efficiency issues. It can also raise issues regarding consistency, uniformity, and adequacy of aerial lighting.
It can therefore be seen that not only are there situations where a balance between glare/spill control and aerial lighting must be reached, but sometimes efficiency of the fixture must be taken into account. It is difficult to balance all those factors.
Some fixtures have been developed that include special visors that decrease or minimize efficiency loss, or even increase the fixture's efficiency. They improve upon the older, less efficient visor methods by using a reflective or highly reflective inner surface that does not block or absorb light, but rather attempts to capture and control it in a useable fashion to the target. Examples of such visor systems are described in MUSCO® Corporation patent applications, see for example, US publication No. 2006/0198145, now U.S. Pat. No. 7,458,700; US publication No. 2006/0176695; US publication No. 2006/0181882; and US publication No. 2006/0181875, now U.S. Pat. No. 7,789,540.
U.S. Pat. No. 7,458,700 provides an improved method for glare and spill control with some level of playability by selective use of different visor types for key aiming directions. However, the intensity of light available for aerial illumination is limited by the visors because they are designed mainly for spill and glare control. Improvements are still needed for situations where more mid-field playability illumination is desirable.
Mid-field playability applies particularly to what can be called aerial sports (e.g. where a ball, as a part of the game, can move to locations well above the field, sometimes 130 feet or higher). Since typical sports lighting systems have fixtures elevated on poles around the outside of the field, and the fixtures are typically aimed down towards the field, the volume of space above the center of the field (e.g. mid-field) may have substantially less light. This can make it difficult for a player to follow a ball in flight, especially if it moves from higher illumination areas to lower illumination and back to higher illumination, or if the player loses continuous sight of the ball and must reacquire it. This not only reduces the enjoyment of the game, but creates concern for safety.
The diagram of FIG. 1A illustrates this. High intensity sports lighting fixtures 10 elevated over 70 feet in the air on a pole (here one pole A1 is shown), each with a plurality of fixtures 10, are used to illuminate a ball field 2 (see, e.g., FIGS. 2A-E). As indicated in FIG. 1A, normally glare and spill control tries to limit off-field light and direct view of the light source. In other words, the main beam from any fixture 10 on pole A1 would not substantially exceed upper and lower margins R(B) and R(T) in FIG. 1A. Thus, persons substantially outside field 2, like those in and around house 8 near field 2, would not experience a substantial amount of light or perceive substantial intensity from the fixtures. But note in FIG. 1A how a baseball, for example hit by batter 6A, might well travel along arc 9. The ball would be quite visible between batter 6A and upper beam limit R(T) because it would be traveling in the main beam. However outfielder 6B may lose track of the ball if it travels above beam limit R(T) because of lack of adequate illumination above limit R(T). Even though the ball might re-enter the beam (or another beam) prior to reaching outfielder 6B, this can be a problem. It can be a very real safety issue for outfielder 6B (e.g. a baseball could hit an outfielder in the head, or players could run into one another because of confusion over flight or location of the ball).
This lack of sufficient aerial lighting can occur even with many lighting fixtures aimed at the playing field from different directions. As indicated in the baseball field example of FIG. 2A, there is a particular risk of insufficient aerial lighting at the middle of the field, as well as from the middle towards the outfield. The dark straight lines in FIG. 2A indicate central aiming axes/directions of beams from plural fixtures on each of eight poles around the field. If most of the fixtures use visors or other conventional glare and spill light control features, ball flight could extend over the top margin R(T) of the beam of each fixture and present aerial illumination issues. As mentioned earlier, visors or louvers designed for glare and spill, even efficient visors that do not negatively impact illumination at the target, have at least three inherent issues that impact playability or aerial illumination.
First, they tend to be designed to cut off the light beyond the target to attempt to contain the light within the target boundary. With these what might be called fully or semi-shielded fixtures, zero or very minimal direct light is directed upward and is not sufficient for playability. For example, these types of systems tend to allow less than 0.5 foot-candle vertical (fcvert) in the 120 to 140 foot elevation range, where baseballs frequently travel; and more frequently allow from zero to 0.2 fcvert. As a result, only indirect up-light reflected off the field surface (e.g. generally accepted in the art as 15 percent for grass), is available for aerial illumination and viewing. However, reflected light off the target surface is dispersed in a generally uncontrolled manner and significantly diminishes with distance. Past experience has proven that indirect up-light reflected off the target surface is generally not sufficient for aerial viewing, unless an unusual highly reflective material, white rock for example, with much higher reflectivity than grass is used. Even when minimum direct light and reflected light are combined, aerial light intensity is often still inadequate for playability, especially at mid field.
Second, if glare and spill control is lessened, it may result in more light being dispersed vertically; even to the point of providing sufficient up-light for playability. One such method to achieve this is to aim the beams less steeply down from horizontal, thus providing higher intensity near horizontal. However, this will likely result in very undesirable offsite glare and spill light, even to the point of causing glare and spill problems similar to those of a fixture with no glare control (e.g. no visor or louvers). Up-light (aerial illumination) provided without louvers or visors, also disperses some light vertically, and thus can sometimes provide satisfactory aerial illumination—but with added difficulty in aerial viewing due to higher intensity viewed at a lower plane. For example, compare vertical foot-candles at 40′ elevation between FIG. 3A (using MUSCO® Corporation's commercially available SportsCluster-2® fixture, having some glare and spill control but without louvers or visors) and FIG. 3C, an exemplary embodiment of the present invention. The difference is 9.25 fcvert in FIG. 3A and 4.80 fcvert in FIG. 3C. The relatively high intensity at 40′ in FIG. 3A can affect the ability to perceive a ball at much higher elevation, even if there is otherwise acceptable aerial light at the higher level (i.e., because of the significant difference between light levels at low elevation and high elevation). Compare this with FIG. 3C, where less than 3 fc difference exists between 40′ and 150′. Note also in FIG. 3A that light levels above 80 feet are not very consistent. In addition, without visor or louvers, the high intensity lamp arc source is visible to viewers both on the target area and offsite. The arc tube is an extremely intense source of glare and should be shielded from viewers when possible. The amount of light intensity needed to view aerial objects is directly proportional to the intensity that is present in normal viewing directions, although considerably less intense. As the intensity at normal directions increases, the amount of light needed for aerial viewing also increases, making it difficult to balance both needs. In contrast, with proper glare and spill control the intensity at normal viewing plane is reduced, thus requiring proportionally significantly lower aerial illumination. In other words, the more light at lower normal viewing directions, the more light needed above them to provide adequate viewing of aerial objects. Additionally, up-light provided by all the means described above is based on the physics of light dispersing vertically, with higher intensity levels near the target plane (e.g. the playing field surface) and diminishing in intensity with elevation. This can create a bright-dark-bright effect for objects in flight that rise through elevation and descend back down. Inconsistent light levels decrease the viewer's ability to track objects in flight. In addition, at higher elevations the light may diminish below acceptable levels, causing the object to be temporarily lost from view.
Third, even if a fixture provides some reasonable amount of up-light for playability, and also provides some reasonable amount of glare and spill control, it is difficult to do so without substantial decrease in efficiency of the light fixture.
Therefore, a need has been identified in the art for a lighting fixture or method that provides more consistent, effective aerial illumination while also providing a substantial amount of glare and spill light control.